Prokaryotic and eukaryotic cells respond to enviromental stress by the induction of a variety of stress-related proteins. In mammalian cells, the most well characterized group of stress proteins are induced by hyperthermia. Transcription of heat shock proteins increases markedly after hyperthermia and several of these genes have been cloned from HeLa cells in other laboratories. It is likely that transcription of other genes is also induced in mammalian cells since approximately 10-20 genes are induced in prokaryotes and lower eukaryotes. One approach to isolate such transcripts is to enrich for heat shock specific cDNA's by hybridization subtraction with mRNA from control cells. We have done this with rodent cells, V79, and we have also constructed a cDNA library from heat shock treated (HS) cells. Our results indicate that the most abundant transcript induced by HS in V79 and CHO cell lines is a small repetitive genetic element. The transcripts of this repetitive element are polyadenylated as are most mRNA species. Transcription of this repetitive element has previously been found to be increased in transformed rodent cells and rodent tumor cells. It is of interest that HS proteins are usually elevated in transformed cells. Sequence analysis of this element reveals that a region has very close similarities to the HS promoter consensus sequence of Drosophilia. The induction of this gene is not non-specific since equitoxic of x-rays or UV-radiation do not increase transcription. We have also isolated cDNA clones for most of the major heat shock protein genes in Chinese hamster cells.